The present invention relates generally to the field of thermal dissipation devices and, more particularly, to a method and apparatus for improving the efficiency of a thermal cooling apparatus in an electronic device.
Thermal dissipation devices are present in a wide variety of applications. Such devices generally employ conduction, convection, or a combination of conduction and convection to dissipate heat generated by a heat source. Conduction is the transfer of heat by the movement of heat energy from a high temperature region to a low temperature region in a body. Convection is the transfer of heat from the surface of a body by the circulation or movement of a liquid or gas over the surface.
These thermal dissipation devices are often used to cool mobile, server, and desktop applications. One example of such an application in which thermal dissipation devices are used is an electronic device such as a microprocessor. Heat can be dissipated from an electronic device through the outer surfaces of the device into the ambient atmosphere.
Currently, in many applications, an electronic device is coupled to a heat pipe that is coupled to a heat sink. Heat generated by the device is transferred through the heat pipe into the heat sink. The heat sink, which is typically a mass of material (usually metal), draws heat energy away from the heat source by conduction of the energy from a high-temperature region to a low-temperature region of the metal. The heat energy can then be dissipated from a surface of the heat sink to the atmosphere by convection.
A well-known technique of improving the efficiency of a conductive heat sink is to provide a greater surface area on the heat sink so that more heat can dissipate from the heat sink into the atmosphere by natural (or free) convection. Increased surface area is typically provided by fins that are formed on a base portion of the heat sink. The thermal efficiency of a heat sink can be further increased by employing forced convection wherein a flow or stream of air is forced over and around the surface of the heat sink.
As the number of components in electronic devices increases, or as the power requirements or operating speeds of the electronic devices increases, the amount of heat generated can increase to a point where conventional heat sink and air convection solutions are inadequate. For example, the airflow required to dissipate the greater level of heat can become excessive, or the physical size of the heat sink required to dissipate the heat can become prohibitive for the particular application.
In the case of portable electronic devices, a balance must be struck between the size of the entire thermal dissipation apparatus and the amount of heat that needs to be dissipated by the device. High power portable electronic devices may generate a great deal of heat, but the portable nature of the device requires the size of the thermal dissipation apparatus to be quite small. One way to achieve this balance is to replace the heat pipe with a vapor chamber to transfer the heat energy from the electronic device to a heat sink. This method is preferred for two reasons. First, the vapor chamber has better mechanical rigidity due to its flat and square shape. A heat pipe, on the other hand, generally has to be physically modified from a cylindrical shape to a rectangular shape. Second, a vapor chamber has better thermal performance.
Vapor chambers have generally been used in the cooling of server applications. In these applications, the vapor chamber and/or heat sink sits on top of the heat source or die. This is not feasible in portable electronic devices since the heat sink is preferably located away from the heat source because of overall package size constraints. For example, the overall stack up height of the thermal dissipation device is usually limited by the relatively small housings of portable devices such as notebook computers. Also, it is generally desirable to use the atmospheric air outside of the portable electronic device to draw the heat convectively away from the vapor chamber.